readme: add an entry about the {obsolete} template change
(It should have been included into the parent changeset.
--- a/README Fri Sep 09 16:42:41 2016 -0700
+++ b/README Sat Sep 10 13:26:19 2016 +0200
@@ -56,6 +56,10 @@
Changelog
=========
+5.5.0 --
+
+ - The {obsolete} template now yield "obsolete" or "".
+
5.4.1 -- 2016-08-01
- compat with Mercurial 3.9